1. Field of the Invention
The present invention relates to solid golf balls having a center, a mid layer, a cover and dimples.
2. Description of the Related Art
Golf balls have numerous dimples on the surface thereof. The dimples disrupt the air flow around the golf ball during flight to cause turbulent flow separation. By causing the turbulent flow separation, separating points of the air from the golf ball shift backwards leading to the reduction of a drag. The turbulent flow separation promotes the displacement between the separating point on the upper side and the separating point on the lower side of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. The reduction of a drag and the enhancement of the lift force are referred to as a “dimple effect”. Excellent dimples disturb the air flow more efficiently. Excellent dimples make a great flight distance.
It is known to those skilled in the art that a great dimple effect is obtained in golf balls on which dimples are densely arranged. A variety of proposals for the purpose of enhancement of the dimple effect have been made with respect to dimple patterns.
U.S. Pat. No. 5,080,367 (JP-A-50-8630) discloses a golf ball with numerous dimples having a uniform size. In this golf ball, most dimple pairs have a pitch of smaller than 0.065 inch. In this golf ball, a relationship between a pitch and a dimple diameter is not considered. In comparison with general dimple diameters, the pitch of 0.065 inch is not sufficiently small. In a pattern with dimples having a uniform size, diameters of the dimples can not be set to be great. The dimples of the golf ball are not arranged densely enough.
U.S. Pat. No. 4,813,677 (JP-A-62-192181) discloses a golf ball with large dimples and small dimples. In this golf ball, high density of dimples is achieved by arranging small dimples in a region which is surrounded by multiple large dimples. However, the small dimples are not sufficiently responsible for the dimple effect.
U.S. Pat. No. 5,292,132 (JP-A-4-347177) discloses a golf ball in which dimples are arranged such that any rectangle having a determined size can not be formed on the land. In this golf ball, small proportion of the land is achieved by arranging numerous small dimples. However, the small dimples are not sufficiently responsible for the dimple effect.
The golf players place great importance also on spin performance of golf balls together with flight performance. Great back spin rate results in small run. For golf players, golf balls which are liable to be spun backwards are apt to be rendered to stop at a targeted position. Great side spin rate results in easily curved trajectory of the golf ball. For golf players, golf balls which are liable to be spun sidewise are apt to allow their trajectory to curve intentionally. The golf balls that are excellent in spin performance are excellent in control performance. High-level golf players particularly place great importance on control performance upon shots with a short iron. In addition, the golf players place great importance on feel at impact of golf balls. Control performance and feel at impact depend on a structure of the golf ball. JP-A-2000-225209 discloses a golf ball having a core, an inner cover, an outer cover and dimples with special specification.
Requirements by golf players concerning flight performance, control performance and feel at impact have been escalated. Golf balls still have room to be improved. An object of the present invention is to provide a golf ball that is excellent in performances.